X 2191. SEX UAL CHARACTERS IN THE R UDDYD UCK—WETMORE. 481 



The internal structure of the larynx m the male ruddy duck is 

 peculiar. Behind the rima glottidis (fig. 1, 6) on either side is an 

 elongate cushion of connective tissue from which a somewhat trian- 

 gular elevation projects into the cavity of the larynx (fig. 1, c). 

 These pads may be called the pulvini laryngis. In addition there is a 

 flap of connective tissue developed along the median luie of the thy- 

 roid cartilage for the length of the larynx. This flap is between 4 and 

 5 mm. high and is bent over toward the left side. It is not men- 

 tioned certainly in anatomies save by Sir Richard Owen ^ who speaks 

 of findmg it ui "the Pelican, the Gigantic Crane, and most of the 

 Rasores." I have called it the ligula laryngis. Apparently it has 

 the same function as the mammalian epiglottis. 

 From a study of the larynx in fresh birds I believe 

 the probable mechanics of inflatmg the tracheal 

 air-sac to be as follows: The male ruddy duck 

 about to display fills the air-sacs of the pulmo- 

 nary series with au\ The rima glottidis is then 

 closed by the action of muscles controllmg the 

 arytenoid cartilages. This bruigs the pomts of 

 connective tissue (jjulvini laryngis) in the larynx 

 together and these with the ligula close the 

 larynx save behind. With the stemo-tracheal 

 and cucullaris muscles relaxed a slight con- 

 traction of the respiratory muscles would in- 

 flate the tracheal air-sac. Though no sphincter 

 muscle is present, contraction at the anterior at- 

 tachment of the sterno-tracheales may close the 

 aperture of the air-sac by pressing the esophagus against it. The 

 release of this pressure and contraction of the broad dermal muscle 

 would serve to deflate the sac. 



The tracheal air-sac is absent in females. The deeper layer of the 

 muscle cucullaris too is less in bulk than in males and the sterno- 

 tracliealis shows no unusual broadening. In a young male about 10 

 days old, however, a tracheal sac was present that measured when 

 inflated 18 mm. long by 15 mm. wide (Cat. No. 224830, U.S.N.M.). 

 It was placed as in the adult male. From examining this bird it was 

 apparent that the sac grows by backward expansion from the openuig 

 in the trachea. Tlie development of the sterno-tracliealis muscle in 

 the 3^oung bhd was extraordinary. It spread over the entire ventral 

 surface of the sac, covering it completely. 



Adult males that were seen in display swam about with swelling 

 breast and neck drawn in, turning or alternately advancing and 

 retreating before the females. At short intervals the head was 



1 Owen, Richard, Comparative Anatomy and Physiology of Vertebrates, vol. 2, 1866, p. 219, 

 65008°— Proc.N.M.vol.52— 17 31 



Fig. 1.— Longitudinal 

 section of larynx of 

 MALE Ruddy duck 



FROM BELOW (X2). 6, 



Rima glottidis. c, 



PULVINUS laryngis, 



d. Mouth of aik-sac. 



